A hernia is a protrusion of a tissue, structure, or part of an organ through the muscle tissue or the membrane by which it is normally contained. Abdominal hernias are one common type of hernia. In an abdominal hernia, a weakness in the abdominal wall grows into a hole, or defect. Tissue may protrude from the defect. Example hernias include umbilical hernias, in which intra-abdominal contents protrude through a weakness at the site of passage of the umbilical cord through the abdominal wall, and incisional hernias, which occur in an area of weakness caused by an incompletely-healed surgical wound. Those of ordinary skill in the art will appreciate that there are other types of hernias in addition to those specifically mentioned herein.
In order to treat a hernia, such as an umbilical or incisional hernia, a doctor may insert a specially designed patch into an incision near the defect. Such a patch is typically designed to be larger than the defect to ensure adequate coverage. The patch is folded or pushed through the incision. In order to allow the patch to be positioned a hernia patch may include positioning straps, which the doctor pulls on to flatten the patch once it is inside the abdominal wall. The patch is maneuvered into a flat position and moved into a suitable position, as described in more detail below. After the doctor is satisfied with the placement of the patch, the patch may be secured by suturing the positioning straps to the margins of the defect, or by suturing a part of the body of the patch to the connective tissue. Any excess material on the positioning strap is then removed and the incision is closed.
One conventional type of hernia patch is made up of a round base for the patch formed from a number of layers. For example, FIG. 1A and FIG. 1B depict an example conventional hernia patch 100. An example alternative hernia patch is made by, e.g., C.R. Bard, Inc. Warwick, R.I., such as the Ventralex™ hernia patch. As shown in FIG. 1A and FIG. 1B, the base of the hernia patch 100 may be composed of three permanent polymer base layers 105; 110, 120. One of the base layers 120 may be made of low porosity expanded polytetrafluoroethylene (ePTFE) film material, and the second and third base layers 105, 110 may be a polypropylene filament knitted mesh. The smooth ePTFE polymer film layer 120 is intended to act as a non-porous tissue separating layer for blocking and preventing visceral organs from coming into direct physical contact with the polypropylene polymer filament mesh layers 105, 110. The second and third base layers 105, 110 can be formed of a single piece of material, folded over to create the two layers as described below.
One shortcoming of the polymeric-only materials used in some conventional hernia patches is that they may fracture, crack, break, and/or separate when subjected to bending, either during surgical installation, handling, insertion, and fixation, or experience the same mechanical failure after a period of time following insertion due to abdominal wall tension, flexion, compression, and/or stretching. When such common polymer hernia repair materials begin to experience material failure due to mechanical manipulation and disruption, material separation of these components can lead to the formation of sharp edges, which can abrade, irritate, and/or perforate adjacent organ tissue in and around the vicinity of the hernia repair.
In the conventional hernia patch 100, a perimeter 122 of the base is composed of a layer of densified polypropylene bonded to a layer of ePTFE film to create the ePTFE polymer film layer 120. As a result, the perimeter 122 has a high degree of radial and planar stiffness, with a relatively high material density (e.g., when composed of a solid polymer).
As utilized herein, the term “stiffness” is intended to have its conventional definition of a measurement of the resistance of an elastic body to deformation when a force is applied along a given degree of freedom. Likewise, as utilized herein, the terms “flexibility” and “elasticity” relate to the ability of a material to elastically deform when a force is applied along a given degree of freedom, but not plastically deform. A material or structure is considered to be flexible as utilized herein when the material or structure deforms with application of force, but when the force is removed, the material returns to its original shape prior to the application of force, without the requirement of heat. That is, the flexible or elastic material is not a shape memory material, which can return to its cold forged shape but only after application of heat.
This relative stiffness of the conventional hernia patch 100 means that the conventional hernia patch 100 takes its own shape and does not conform itself well to the contours of tissue, such as a patient's abdominal wall. While it does have some flexibility, such that it can be folded in half during implantation and then it will return to its original shape once the force is removed, it does not have a sufficiently high relative amount of flexibility or elasticity to respond well to the much smaller forces applied to the patch 100 as it is pressed up against a tissue wall. Further, because the densified perimeter 122 polymer structure does not possess or exhibit a sufficient macro porosity for tissue in-growth, thereby permanently limiting the material from becoming incorporated by remodeling tissue involved in healing at the implant site, these non-conforming structures often become at risk for mechanical disruption, material contraction, and/or device protrusion into other surrounding tissues following implantation. This lesser degree of tissue in-growth or cellular incorporation often leads to material encapsulation involving chronic inflammation and stimulation of dense, a-cellular connective tissue implicated in visceral organ adhesion formation between the non-porous polymer portion of the patch and the abdominal wall. Such undesirable non-healing effects have further been implicated in published reports of higher reoccurrence rates of the primary hernia repair, chronic pain, and subsequent reintervention requirements to surgically repair the post operative complication.
In the example conventional hernia patch 100, some of its high degree of stiffness results from the existence of a monofilament polymeric stiffening ring 130 that is attached, or stitched into the periphery of the base between the two base layers 105, 110, inside of a pocket 150 formed therebetween. The stiffening ring 130 is sewed or permanently locked into position between the two mesh layers 105, 110. The stiffening ring 130 may be a memory material that memorizes a shape and returns to the memorized shape after being subjected to deformation. This may allow the conventional hernia patch 100 to unfold or open immediately following folded insertion through an incision. For example, in one type of hernia patch, the stiffening ring is made of either an extruded monofilament or molded polyethylene terephthalate (PET) ring that is stitched into the periphery of the mesh base between the two polypropylene mesh layers (105 and 110). The stiffening ring 130 is held in tight proximity to the base materials by peripheral stitching. Alternatively, the stiffening ring 130 may be embedded in one of the base layers.
In the conventional hernia patch 100, positioning straps 140 are attached to the above-described layers of mesh to facilitate placement and fixation. The positioning straps 140 transition from the polypropylene base layer 110, and the positioning straps 140 are a continuation of the same piece of mesh as the polypropylene base layer 110.
In the example conventional hernia patch 100, a slit exists in the polypropylene mesh layer 110 between the two positioning straps 140. This slit provides an opening into a pocket 150 between the polypropylene mesh layers 105, 110. When the positioning straps 140 are placed under tension, such as by pulling the straps 140 apart, the slit opens and the pocket 150 becomes accessible. A doctor may use the pocket 150 with either a finger or instrument to further deploy, flatten out, or to position the conventional hernia patch 100 once the conventional hernia patch 100 is inserted into the incision.
The conventional hernia patch 100 is stitched in two locations. An interior stitching 160 is provided in an interior part of the patch, located between the point where the straps 140 transition into the polypropylene base layer 110 and the stiffening ring 130, but still close or proximal to the stiffening ring. This interior stitching penetrates through all three base layers 105, 110, 120. An outer stitching 170 is provided between the stiffening ring and the periphery of the conventional hernia patch 100. This peripheral stitching penetrates through the two polypropylene mesh base layers 105, 110, but not the ePTFE base layer 120.
Due to the above-described configuration of the stiffening ring 130, positioning straps 140, pocket 150, and stitching 160, 170 in the conventional hernia patch 100, the above-described shortcomings regarding positioning the patch 100 and conforming the patch to the contours of the patient's abdominal wall may exist. Because the stiffening ring 130 is fixed to the base layers 105, 110, 120 via the interior stitching 160, the straps 140 transition into the polypropylene base layer 110, and a slit exists in the polypropylene base layer 110 between the straps 140, when tension is applied by the straps as they are pulled up and out through the hernia defect for suture fixation outside of the abdominal cavity, but within the incision of the abdominal wall, the center of the conventional hernia patch 100 pulls up into the hernia defect while the perimeter of the conventional hernia patch 100 tends to separate away from the tissue wall adjacent to the hernia defect with which it is meant to be in direct contact. This creates a large open space between the polypropylene base layers 110 and 105 that can delay tissue in-growth and healing. When this required tension is applied to these straps for device positioning and fixation, it causes significant separation of the material layers and formation of the pocket 150. The indwelling intra-abdominal cavity portion of the base layer material of the conventional hernia patch 100 tends to yield to the tension applied by the positioning and fixation straps by stretching upward, lifting and bending away from the abdominal wall. This creates a non-uniform and/or irregular shaped surface profile that is often a substantially conical shape in appearance, leaving an undesirable gap or open space between the perimeter body of the conventional hernia patch 100 and the abdominal wall. This space becomes difficult for tissue to heal across, thereby requiring greater lengths of time for connective tissue to fill in between the perimeter rim of the patch. Such spaces can further lead to complications of visceral organ entrapment involved with adhesion formation.
In a 28-day swine preclinical study, the limitations of a conventional hernia patch were confirmed. A conventional hernia patch was implanted into midline hernia detects of a swine test subject, and laparoscopic images were taken at days 1, 7, 14, and 28 post-implantation. At 28 days, the patch was explanted and gross explant photographs were taken.
Images of the conventional hernia patch (see FIG. 7B) show that after 24 hours in-vivo, a space was formed between the perimeter of the conventional hernia patch and the tissue above the patch. Cross sectional photographs taken at explant 28 days after implantation (see FIG. 8B), large spaces continued to exist between the perimeter of the conventional patch and the abdominal wall.